1. Field of the Invention
The present invention relates to a combustion heater system for use in a motor vehicle, and more particularly to a combustion heater system having a control unit for controlling the ignition and extinction of a combustion heater which utilizes the heat of combustion of a fuel in a motor vehicle with a clean power plant, such as an electric vehicle.
2. Description of the Prior Art
FIG. 4 of the accompanying drawings shows a conventional combustion heater system for use in a motor vehicle with a clean power plant, such as an electric vehicle. The illustrated combustion heater system has a combustion pad 102 disposed in a combustion chamber 101, a fuel supply passage 104 for supplying a fuel from a fuel tank 103 to the combustion pad 102, a solenoid-operated valve 105 for selectively opening and closing the fuel supply passage 104, a glow plug 106 for heating the combustion pad 102, a fan 107 for supplying air into the combustion chamber 101, and a control unit 108 for controlling the solenoid-operated valve 105, the glow plug 106, and the fan 107.
When the starter switch of the conventional combustion heater system is turned on, the control unit 108 rotates the fan 107 at a half output rate to supply air into the combustion chamber 101 as shown in FIG. 5A of the accompanying drawings, and the control unit 108 energizes the glow plug 106 to pre-glow the combustion pad 102 for 30 seconds, for example, as shown in FIG. 5B of the accompanying drawings. Thereafter, the control unit 108 actuates the solenoid-operated valve 105 to open the fuel supply passage 104 for thereby supplying the fuel to the combustion pad 102 as shown in FIG. 5C of the accompanying drawings. The control unit 108 continues to energize the glow plug 106 for 60 seconds, for example, to heat the combustion pad 102 up to a temperature at which the fuel can be ignited. When the fuel supplied to the combustion pad 102 is ignited by spontaneous combustion, the control unit 108 de-energizes the glow plug 106. After having waited for 20 seconds, for example, until the combustion of the fuel is stabilized, the control unit 108 rotates the fan 107 at a full output rate.
When the starter switch of the conventional combustion heater system is turned off, the control unit 108 inactivates the solenoid-operated valve 105 to close the fuel supply passage 104 for thereby stopping the supply of the fuel to the combustion pad 102 to extinguish the same as shown in FIG. 6B of the accompanying drawings. As shown in FIG. 6A of the accompanying drawings, the control unit 108 rotates the fan 107 at a full output rate to discharge any unburned gas from the combustion chamber 101. After elapse of a predetermined period of time, the control unit 108 turns off the fan 107. In some combustion heater systems, the fuel is extinguished by inactivating the fan to stop supplying the air into the combustion chamber, or the fuel is extinguished by stop supplying both the fuel and the air.
With the above conventional combustion heater system, however, when the fuel is to be ignited, the air is continuously supplied to the combustion chamber 101 by the fan 107 until the fuel supplied to the combustion pad 102 is ignited, i.e., from the time at which the fuel is supplied to the time at which the fuel is ignited by spontaneous combustion. Therefore, before the fuel is ignited, the fuel supplied to the combustion pad 102 is vaporized and discharged, resulting an undesirable unburned fuel emission. In addition, since the air required for the fuel to be combusted is supplied while the glow plug 106 is being energized, the glow plug 106 is deprived of heat by the air flow. As a consequence, a certain amount of electric energy is wasted by the glow plug 106, and a relatively long period of time is consumed before the fuel is ignited.
When the fuel is to be extinguished, the supply of the fuel to the combustion pad 102 is stopped. However, because the fan 107 is continuously actuated, the amount of heat and the amount of supplied air are brought out of balance. Though the flame is put out, the fuel attached to the combustion pad 102 is vaporized by the supplied air and discharged out of the combustion chamber 101. If the supplied air is stopped to extinguish the fuel, then the flame is put out, and the fuel remains unburned in the combustion pad 102. The remaining fuel is vaporized by the heat of the combustion pad 102 and discharged out of the combustion chamber 101.
Therefore, the conventional combustion heater system tends to produce a large amount of unburned fuel emission when the fuel is ignited and extinguished.
Japanese patent publication No. 57-40418, published Aug. 27, 1982, discloses an apparatus for controlling a heated water source in a combustion heater system for use in an automobile.